JPH0737703A - Positive temperature characteristic resin composition - Google Patents

Abstract

PURPOSE:To give heat resistant characteristics, stability of resistance and variability of resistance rising temperature of a PTC resin composition. CONSTITUTION:A non-crystalline thermoplastic resin of 30 to 90 volume % is included as a matrix resin and a conductive powder of 70 to 10 volume % ia dispersed thereto. Here, it is also possible to use, as the matrix resin, a material mixing the non-crystalline thermoplastic resin of 50 to 99 volume % and a denaturing agent of 50 to 1 volume % for changing thermal characteristic of the non-crystalline thermoplastic resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin composition having a positive temperature coefficient whose resistance value changes with temperature having a positive temperature coefficient, and more particularly to improvement of a matrix resin.

[0002]

2. Description of the Related Art Conventionally, a composition in which a conductive powder such as carbon black is dispersed in a matrix of a crystalline polymer such as polyethylene or fluororesin has a positive organic temperature characteristic (hereinafter referred to as "PTC"). ) It is common as a composition. Here, the use of a crystalline polymer as the matrix utilizes the rapid volume expansion accompanying the melting of crystals near the melting point to cut the links formed by the conductive particles and to reduce the spacing between particles. This is to utilize the property of increasing the resistance value by expanding.

[0003]

However, when the above-mentioned crystalline polymer is used as a matrix resin, the resin is liquefied at the melting point or higher, so that the resistance tends to be lowered. Therefore, if the resin composition is heated above the resistance peak temperature, the resistance value may decrease, the current may increase, and damage may occur. Further, when heated to near the melting point, it is likely to be deformed, and therefore, when the temperature is returned to room temperature, the resistance value may change from the resistance value before the temperature rise.

Therefore, as a countermeasure against these problems, in order to suppress the molten state above the melting point, the matrix resin is subjected to electron beam crosslinking or chemical crosslinking with an organic peroxide,
In addition, addition of another crystalline polymer having a different melting point is performed. However, electron beam cross-linking is expensive in equipment, and it is difficult to obtain sufficient cross-linking density in a short time by chemical cross-linking of a thermoplastic polymer alone. When added, the problem that the amount of change in resistance (maximum resistance value / room temperature resistance value) of the PTC resin composition is remarkably reduced is encountered.

Further, as described above, the PTC resin composition using the crystalline polymer has a correlation between the melting point and the resistance rising temperature, so that the resistance rising temperature can be adjusted according to each application. Needs to change the melting point of the crystalline polymer. However, since the melting point is determined by the chemical structure of the polymer itself, crystalline polymers having different structures must be prepared for each required resistance rising temperature. Therefore, it is difficult to adjust the resistance rising temperature to an arbitrary temperature.

Therefore, an object of the present invention is to provide a PTC resin composition which can satisfy the heat resistance, the resistance stability, and the variability of the resistance rising temperature as described above.

[0007]

A PTC resin composition according to the present invention comprises an amorphous thermoplastic resin as a matrix,
The feature is that the conductive powder is dispersed therein.

In the above-mentioned PTC resin composition, preferably, the amorphous thermoplastic resin is contained in an amount of 30 to 90% by volume and the conductive powder is included in an amount of 70 to 10% by volume. If the conductive powder exceeds 70% by volume, it becomes difficult to mix the conductive powder into the matrix resin.
The resistance value becomes too low, and good PTC characteristics cannot be obtained. If the conductive powder content is less than 10% by volume, the resistance value becomes too high and the resistance value becomes close to that of an insulator, and even in this case, good PTC characteristics cannot be obtained.

Further, in the present invention, as the matrix, a mixture of an amorphous thermoplastic resin and a modifier which changes the thermal characteristics of the amorphous thermoplastic resin may be used.

In the PTC resin composition described above, the following composition ratios are preferably selected. That is, in the matrix, the amorphous thermoplastic resin is 50 to 99.
% By volume, and 50 to 1% by volume of the modifier, respectively,
In addition, the conductive powder is contained in an amount of 70 to 10% by volume based on 30 to 90% by volume of the mixture of the amorphous thermoplastic resin and the modifier. Here, if the amount of the modifier exceeds 50% by volume, the proportion of the amorphous thermoplastic resin exhibiting the PTC characteristic in the matrix resin decreases, and good PTC characteristics cannot be obtained. In addition, the denaturant is 1% by volume
When it is less than the above, the change in the thermal characteristics of the amorphous thermoplastic resin due to the effect of the modifier to be added is small and the rise temperature of the resistance of the PTC does not change. Further, as in the case where the above-mentioned modifier is not added, if the conductive powder exceeds 70% by volume, it becomes difficult to mix the conductive powder into the matrix resin, and the resistance value becomes too low. , Good PTC
The characteristics cannot be obtained. In addition, conductive powder is 10% by volume
If it is less than the above value, the resistance value becomes too high, and the resistance value becomes close to that of an insulator, and good PTC characteristics cannot be obtained.

In order to obtain a molded product from the PTC resin composition according to the present invention, a solvent is added and mixed to form a paste, and a thick product is prepared on a substrate by screen printing, a doctor blade method or the like, There is a method of heating this, or a method of producing what is heated and melted by extrusion molding, compression molding or the like.

[0012]

In this invention, an amorphous thermoplastic resin is used as the matrix instead of the crystalline polymer, and the volume change due to the crystal melting of the polymer is not caused but the temperature in the vicinity of the softening point from the glass transition point is used. The PTC characteristic is given by the rapid volume change.

[0013]

Therefore, according to the present invention, unlike the conventional crystalline polymer composition, the shape change and the sharp decrease of the resistance value due to the liquefaction of the resin do not occur even at the melting point or higher, so that the resistance value is It is possible to prevent a change from the resistance value before the temperature rise and to prevent damage. In addition, post-treatments such as electron beam cross-linking and chemical cross-linking are not required as measures against these problems.

In the present invention, the amorphous thermoplastic resin has a glass transition point and a softening point by adding a modifier that changes the thermal characteristics of the amorphous thermoplastic resin such as a flexibility imparting agent. It can be lowered, and the degree of the reduction can be arbitrarily adjusted. Therefore, the temperature of the resistance rising point of the PTC characteristic can be adjusted arbitrarily.

If a modifier having reactivity with the amorphous thermoplastic resin is used as the above-mentioned modifier, a cross-linking reaction between the amorphous thermoplastic resins easily occurs, so that the heat resistance of the PTC resin composition is reduced. The reliability such as sex is improved. As the above-mentioned reactive modifier, for example, an epoxy resin, a urethane resin, a silicone resin, or the like is advantageously used.

[0016]

Example 1 As an amorphous thermoplastic resin, two types of polyvinyl butyral (hereinafter "PVB") having different glass transition points (T _g ) and softening points as shown in Table 1 below were prepared. . As the conductive powder, spherical carbon powder having an average particle size of 5 μm was prepared.

[0017]

[Table 1]

Next, the PVB and the carbon powder were treated with the composition ratios shown in Table 2 below according to the procedure shown in FIG.

[0019]

[Table 2]

Referring to FIG. 1, in a raw material mixing step 1, PVB and carbon powder are mixed, and a mixing step 2 is performed.
In, the powders were mixed in a mortar. At this time, butyl carbitol was added as a solvent to obtain a paste-like mixture. Next, in the kneading step 3, the above-mentioned paste mixture was kneaded using a three-roll mill. Next, in printing step 4, PT is made by screen printing.
Printing was performed to form a film of the C resin composition, and then, in drying step 5, a drying treatment was performed at 150 ° C. for 2 hours.

FIG. 2 shows a sample 6 obtained through the printing process 4 and the drying process 5 described above. The sample 6 includes a base material 7 made of polyethylene terephthalate having a thickness of 0.25 mm. On the base material 7, a pair of electrodes 8 and 9 is formed by baking a silver paste. Both of the electrodes 8 and 9 have a thickness of about 20 μm, and the distance between them is 10 mm. The PTC resin composition film 10 is formed so as to extend between the electrodes 8 and 9 as described above. This film is 10mm × 14m
It has a planar dimension of m and its thickness is about 20 μm.

PT of the sample obtained as described above
The C characteristic is shown in FIG. As you can see from Figure 3,
Each sample shows a large increase in resistance between the glass transition point and the softening point, and the decrease in resistance value is very small even in a high temperature region above the temperature of the softening point, which is the peak resistance value.

In Example 1 described above, PV, which is one kind of polyvinyl acetal, is used as the matrix resin.
Although B was used, there are polyvinyl formal and the like. In addition, an amorphous thermoplastic resin such as an acrylic resin can also be used. In addition, as the carbon powder, among various carbon powders such as carbon black and graphite, spherical carbon having a particle size larger (1 to 50 μm) and a shape closer to a sphere than the carbon powder having a small particle size and complicated aggregation. It is more effective to use the powder because the links formed by the conductive particles are easily broken with respect to the volume change of the matrix resin.
Further, instead of the carbon powder, powder having conductivity such as various metal particles such as gold and silver may be used. Note that P
As a solvent for forming the TC resin composition into a paste,
Various organic solvents can be used.

Example 2 As an amorphous thermoplastic resin, PVB having the characteristics shown in Table 3 below was prepared.

[0025]

[Table 3]

As a modifier for changing the thermal characteristics of the amorphous thermoplastic resin, bisphenol A diglycidyl ether, which is an epoxy flexible resin, was prepared. As shown in Table 4 below, the amorphous thermoplastic resin contains no epoxy flexible resin as a modifier,
10, 20, and 30% by volume were added, respectively, and these and spherical carbon powder having an average particle diameter of 5 μm were treated in the same manner as in Example 1 to obtain a sample.

[0027]

[Table 4]

The above-mentioned epoxy type flexible resin has a structure having an epoxy group at the end of a chain structure,
By reacting with B, the chain in the molecular structure of PVB is lengthened, the molecular weight between cross-linking points is increased, and as a result, the cross-linking density is lowered, and flexibility is imparted.

The PTC characteristics of the PTC resin composition in the sample obtained as described above are shown in FIG. 4, and the glass transition point and softening point are shown in Table 5 below.

[0030]

[Table 5]

As can be seen from FIG. 4 and Table 5, the glass transition point and the softening point shift to the low temperature side, and the resistance rising temperature also shifts to the low temperature side, depending on the addition amount of the flexible resin. .

Example 3 As the amorphous thermoplastic resin, PVB having the characteristics shown in Table 3 was prepared as in Example 2.

On the other hand, an epoxy-modified silicone resin, which is a silicone-based flexible resin, was prepared as a modifier for changing the thermal characteristics of this amorphous thermoplastic resin. As shown in Table 6 below, a flexible resin was added to an amorphous thermoplastic resin at 0, 10, 20, and 30% by volume, respectively,
These and spherical carbon powder with an average particle size of 5 μm,
The same process as in Example 1 was carried out to obtain a sample.

[0034]

[Table 6]

The silicone-based flexible resin used in Example 3 also has a structure having an epoxy group in a part of the chain structure as in Example 2, and by reacting with PVB, PVB Lengthening the chain in the molecular structure to increase the molecular weight between cross-linking points, resulting in lower cross-linking density,
It acts to add flexibility.

The PTC characteristics of the PTC resin composition in each sample thus obtained are shown in FIG. 5, and the glass transition point and softening point are shown in Table 7 below.

[0037]

[Table 7]

As can be seen from FIG. 5 and Table 7, also in this Example 3, the glass transition point and the softening point were shifted to the low temperature side according to the addition amount of the flexible resin, and the resistance rising temperature was also changed. It is shifting to the low temperature side.

In the second and third embodiments described above,
As the matrix resin, as in the case of Example 1, P
In addition to polyvinyl acetal such as VB, an amorphous thermoplastic resin such as an acrylic resin can be used. Further, as the flexibility-imparting agent which is a modifier, not only epoxy resin and silicone resin but also urethane resin can be used. These resins have reactivity with the amorphous thermoplastic resin, but a flexibility imparting agent having no such reactivity can also be used. That is, rubber latex or the like does not have reactivity with the thermoplastic resin, but since it is possible to impart flexibility to the matrix resin by forming the dispersed fine particle phase, such rubber latex or the like is also applicable. It can be used as a flexibility imparting agent.
Further, as the conductive powder and the solvent used in Examples 2 and 3, various conductive powders and various organic solvents can be used as in the case of Example 1.

[Brief description of drawings]

FIG. 1 is a process chart showing an example of a procedure for producing a paste of a PTC resin composition according to the present invention.

FIG. 2 is a plan view showing a sample 6 produced to evaluate the PTC resin composition according to the present invention.

FIG. 3 is a diagram showing PTC characteristics of a sample obtained according to Example 1 of the present invention.

FIG. 4 is a diagram showing PTC characteristics of a sample obtained according to Example 2 of the present invention.

FIG. 5 is a diagram showing PTC characteristics of a sample obtained according to Example 3 of the present invention.

[Explanation of symbols]

 10 PTC resin composition film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroshi Nagakubo 2 26-10 Tenjin, Nagaokakyo, Kyoto Prefecture Murata Manufacturing Co., Ltd. (72) Hiromi Yumikura 2 26-10 Tenjin, Nagaokakyo, Kyoto Murata Manufacturing Co., Ltd.

Claims (7)

[Claims] 1. A positive temperature characteristic resin composition comprising an amorphous thermoplastic resin as a matrix and conductive powder dispersed therein. 2. The positive temperature characteristic resin composition according to claim 1, wherein the amorphous thermoplastic resin contains 30 to 90% by volume and the conductive powder contains 70 to 10% by volume, respectively. 3. A positive temperature characteristic resin composition in which a mixture of an amorphous thermoplastic resin and a modifier that changes the thermal characteristics of the amorphous thermoplastic resin is used as a matrix, and conductive powder is dispersed therein. object. 4. The matrix contains the amorphous thermoplastic resin in an amount of 50 to 99% by volume and the modifier in an amount of 50 to 1% by volume, and the conductive powder is the mixture 30 to 90. The positive temperature characteristic resin composition according to claim 3, comprising 70 to 10 volume% with respect to volume%. 5. The positive temperature characteristic resin composition according to claim 3, wherein the modifier is one selected from the group consisting of an epoxy resin, a urethane resin, a silicone resin and a rubber latex. . 6. The positive temperature characteristic resin composition according to claim 1, wherein the amorphous thermoplastic resin is a polyvinyl acetal or an acrylic resin. 7. The positive temperature characteristic resin composition according to claim 1, wherein the conductive powder is carbon powder or metal particles.